Equation of state of tantalum to 174 GPa

The volume compression of tantalum was measured to 174 GPa in a diamond-anvil cell using angle-resolved synchrotron x-ray diffraction. A third-order Birch-Murnaghan equation-of-state constrains the compression data rather well with the zero-pressure isothermal bulk modulus ${B}_{0T}=194.7(4.8)\mathrm{GPa}$ and the first pressure derivative ${B}^{\ensuremath{'}}=3.4(0.1).$ These values are consistent with the previous ultrasonic results, ${B}_{0S}=196\mathrm{GPa}$ and ${B}^{\ensuremath{'}}=3.8,$ but are different from the previous x-ray compression results, ${B}_{0T}=231\mathrm{GPa}$ and ${B}^{\ensuremath{'}}=2.5.$ The current compression data also demonstrate that the bcc phase of Ta continues to be stable to 174 GPa, which qualifies tantalum for a pressure standard in static high-pressure experiments.